While previous research and theory has emphasized the importance of impulsivity in suicidal behavior, the underlying behavioral basis of suicide remains poorly understood, mostly because of methodological limitations. Previous studies examining the relationship between impulsivity and suicidality have relied nearly exclusively on questionnaire-based measures of impulsivity and have lacked adequate consideration of psychiatric diagnosis. This study will use behavioral measures of impulsivity to examine the underlying relationships between impulsivity and a range of suicidal behaviors/risk factors in three groups (n = 84 per group): hospitalized adolescents with high levels of suicidal ideation (Suicide+), hospitalized adolescents with low levels of suicidal ideation (Suicide-), and normal controls with no suicidal ideation recruited from the community (Control). In order to examine state dependent changes in impulsivity related to suicidal ideation, participants will be studied at two points during the time associated with the most dramatic reduction in suicidal thoughts and behaviors (a period spanning up to one week of hospitalization). Participants will be recruited from two major psychiatric diagnostic categories with particularly high incidence of suicidal behaviors: Maior Depressive Disorder (MDD) and Conduct Disorder (CD). Comorbidity of substance abuse will also be taken into account for each of these diagnostic groups. Specifically, we propose to: (1) demonstrate that response disinhibition/attentional behavioral models of impulsivity are more sensitive than reward-choice paradigms to performance differences in hospitalized and non-hospitalized adolescents differing in suicidality; (2) demonstrate that performance on behavioral measures of impulsivity is related to the severity of some (frequency and lethality of suicide attempts, and aggression history) but not other (depression, hopelessness, intent, and precautions to avoid detection) specific suicidal behaviors and risk factors; (3) determine whether changes in suicidality parallel state-dependent changes in impulsivity as measured by behavioral techniques across the hospitalization period; and (4) determine if the relationship between impulsive performance, suicidal symptoms and risk factors generalizes across psychiatric diagnoses (MDD and CD). This study will help answer theoretical questions pertaining to the role that impulsivity plays in suicidality and will also extend validation of current impulsivity methodologies. Establishing the relationship of impulsivity to suicidal behaviors is a necessary foundation for future research that would: (a) enhance the early detection of at-risk groups; (b) relate our understanding of suicide to findings from the emerging literature on the neurobiology of impulsivity; and (c) improve treatment strategies for at-risk groups.